The present invention concerns methods for articles such as garments, fabrics and the like in a liquid carbon dioxide cleaning medium.
Organic solvents such as perchlorethylene and other low-pressure liquid solvents have long been used in cleaning system such as dry cleaning systems. Recently, however, there are growing concerns that these solvents may harm the environment and pose occupational safety hazards. These concerns have led to an extensive search for alternate solvents that are less hazardous, and systems for applying such solvents. Examples are those systems described in U.S. Pat. No. 6,098,430 to McClain et al., and U.S. Pat. No. 5,943,721 to Lerette et al. Other systems are described in PCT Publication WO 99/13148 to Shore et al. and PCT Publication WO 97/33031 to Taricco.
U.S. Pat. No. 5,370,742 to Mitchell et al. (Clorox) describes a liquid/supercritical cleaning system in which a first fluid is removed from contact with the substrate to be cleaned with a second fluid, where the first fluid is a densified gas and the second fluid is a compressed gas.
U.S. Pat. No. 5,904,737 to Preston et al. (MVE, Inc.) describes a carbon dioxide dry cleaning system featuring a pair of liquid carbon dioxide storage tanks, in which the pair of storage tanks are selectively pressurized with a compressor to cause the liquid carbon dioxide to flow through cleaning nozzles in a wash vessel to agitate objects being cleaned therein. However, Preston uses a pump to circulate wash medium to achieve jet aggitation (See column 8, line 57).
PCT Application WO 00/53839 to Carr (Sail Star Ltd) describes a dry cleaning process using rotating basket agitation in which the cleaning chamber is filled by creating a pressure differential and causing carbon dioxide to flow in response to the pressure differential.
PCT Application WO 81/01246 to Witzenburg (Caterpillar Tractor Co.) describes a pumpless flow system for corrosive liquids in which liquid is transported by pressure differential without the need for mechanical pumps.
The present invention provides a method for the pumpless transfer of liquid carbon dioxide cleaning medium in a carbon dioxide dry cleaning apparatus having a wash vessel, a working vessel, a vapor vessel, and a compressor. The apparatus is preferably overpressurized with about 10, 30 or 50 to about 130, 150 or 180 psig of of an overpressurization gas such as air. The method comprises steps of:
(a) storing liquid carbon dioxide dry cleaning medium in the working vessel;
(b) storing a vapor comprising air and carbon dioxide as a gas under pressure in the vapor vessel;
(c) transferring a portion of the vapor from the vapor vessel to the wash vessel, by at least partially equilibrating the pressure between the vapor vessel and the wash vessel, with the wash vessel remaining at a pressure less then that of the working vessel; then
(d) transferring at least a portion of the liquid carbon dioxide cleaning medium from the working vessel to the wash vessel by the force of a pressure differential therebetween;
(e) washing articles to be cleaned in the wash vessel while concurrently
(f) circulating at least a portion of the liquid dry cleaning medium (i) from the wash vessel to the working vessel by compressing vapor from the working vessel into the wash vessel with the compressor, and then (ii) from the working vessel back to the wash vessel by compressing vapor from the wash vessel into the working vessel with the compressor. Preferably the apparatus further includes a filter, and the aforesaid circulating is carried out at least in part through the filter.
In one embodiment, step (d) of transferring at least a portion of the liquid carbon dioxide cleaning medium is carried out by providing a difference in elevation between the working vessel and the wash vessel.
In another embodiment, step (d) of transferring at least a portion of the liquid carbon dioxide cleaning medium is carried out by: (i) transferring liquid carbon dioxide cleaning medium from the working vessel to the wash vessel by the force of the pressure differential between the working vessel and the wash vessel (referred to as xe2x80x9cPDPVxe2x80x9d below); and then (ii) transferring liquid carbon dioxide cleaning medium from the working vessel to the wash vessel by compressing vapor into the working vessel with the compressor to create a pressure differential between the wash working vessel and the wash vessel, with the cleaning medium transferring in response to the pressure differential. Transferring step (ii) may be carried out by compressing vapor from the vapor vessel into the working vessel, or may be carried out by compressing vapor from the wash vessel into the working vessel.
In another embodiment, step (d) of transferring at least a portion of the liquid carbon dioxide cleaning medium is carried out by: (i) compressing vapor from the vapor vessel into the wash vessel with the compressor; and then (ii) transferring liquid carbon dioxide cleaning medium from the working vessel to the wash vessel by compressing vapor into the working vessel with the compressor to create a pressure differential between the wash working vessel and the wash vessel, with the cleaning medium transferring in response to the pressure differential. The transferring step (ii) may be carried out by compressing vapor from the vapor vessel into the working vessel, or may be carried out by compressing vapor from the wash vessel into the working vessel.
In one embodiment of the invention, the transferring step (c) is preceded by evacuating at least a portion of the air from the wash vessel
In another embodiment of the invention, the transferring step (c) is preceded by (directly or indirectly) adding carbon dioxide to the wash vessel (e.g., to make up for carbon dioxide lost during a previous cycle).
In another embodiment of the invention, the washing step (e) is followed by the steps of: (f) transferring the liquid carbon dioxide cleaning medium from the wash vessel to the working vessel by the force of a pressure differential created with the compressor; and then (g) transferring the vapor from the wash vessel to the vapor vessel with the compressor. When the transferring step (c) is completed, there is typically a final venting of carbon dioxide, the loss of which may be made up prior to the next cycle as noted above.
As noted above, the apparatus preferably further comprises a filter. In such a case, the method preferably further comprises the steps of: filtering the liquid carbon dioxide cleaning medium through the filter between washing steps and independently of the wash vessel by the force of a pressure differential created with the compressor. The filtering step may be carried out by transferring the liquid carbon dioxide cleaning medium between the working vessel and the vapor vessel. More particularly, the filtering step may be carried out by (i) transferring the liquid carbon dioxide cleaning medium from the working vessel to the vapor vessel through the filter by the force of a pressure differential created with the compressor, and then (ii) draining the liquid carbon dioxide cleaning medium from the vapor vessel back to the working vessel. In the alternative, the filtering step may be carried out by (i) transferring the liquid carbon dioxide cleaning medium from the working vessel to the vapor vessel through the filter by the force of a pressure differential created with the compressor, and then (ii) transferring the liquid carbon dioxide cleaning medium from the vapor vessel back to the working vessel by the force of a pressure differential created with the compressor.